The present invention relates to an electrostatic spray device for coating powder. It relates more particularly to a device having a powder channel, the downstream end of which has a spray opening for the spraying of the coating powder. At least one gas channel with at least one gas outlet is arranged substantially in the radial center of said powder channel upstream of its spray opening, the gas outlet discharging axially in the direction toward the spray opening. At least one electrode, around which gas from the gas channel flows, is located in the gas outlet opening, the downstream electrode end of the electrode terminating substantially at the downstream end of the gas outlet.
One prior art electrostatic spray device is disclosed in U.S. Pat. No. 4,289,278. In this known spray device, a stream of gas flows around an electrode in the powder channel so that no particles of powder will deposit on the electrode. In this prior art device it is unimportant whether the electrode is located within a gas channel; or whether the electrode lies in the stream of powder and a stream of gas which keeps the electrode powder-free is fed to the stream of powder. Also, in the prior art device, the electrode is located relatively far upstream of a spray opening for the coating powder, so that the flow situation at the spray opening has no influence on the action of the electrode. In another embodiment, the electrode is located in the center of a spray opening which widens in the direction of flow.
In another electrostatic spray device, disclosed in U.S. Pat. No. 4,380,320, the powder channel has a portion of reduced cross-section, the spray opening adjoining the downstream end of this portion. A support extends axially through the powder channel and through the spray opening, the support bearing an electrode axially at its front end outside the spray opening. A gas channel passing axially through the support debouches into the spray opening in an annular nozzle formed in the support, the nozzle being directed radially outward against the wall of the spray opening which widens in funnel-like manner in the direction of flow. The spraying of the powder is effected by the impinging of the star-shaped radial stream of gas on the powder channel stream of annular cross-section in the spray nozzle.
Additional electrostatic spray devices, which do not suggest the features of the present invention, are disclosed in Federal Republic of Germany OS-16 52 421, OS-23 12 363, OS-27 20 458 and OS-33 10 983, and Swiss Patent 609 585. U.S. Pat. No. 3,940,061 shows an electrode arranged in the center of a spray opening of an electrostatic spray device, with air flowing around the electrode.